1. Technical Field
The present invention relates to a method for use in a cellular communication network as well as to a corresponding cellular communication network.
2. Description of Related Art
In existing third generation (3G) cellular networks if the connection (Iu interface) between the Radio Network Controller (RNC) and Core Network fails or if there is an outage in the Core Network, the customers do not get any service. More importantly, they normally will not be aware of this situation, because their user equipments (UE) are still camping on the 3G network as the radio access network is still radiating system information elements. So, in cases of Iu breakdown or Core Network outage due to whatever reason, the RNC keeps providing coverage but no service to the UEs under its control. This means that these UEs are camping on the 3G network but they cannot access the network for service.
One possibility to overcome this problem would be to switch the RNC off. This would have as a result that most UEs in the coverage area of the RNC select an alternative cellular communication network to connect to, if available, for example a second generation (2G) cellular network. Furthermore, the UEs that are not able to select another network, for example because the alternative network does not permit them to be connected, would at least be aware that there is no service, because the radio access network would not be radiating any system information elements. However, a high number of UEs would attempt to select the alternative cellular communication network at the same time, resulting in many simultaneous Location Update Requests/Routing Area Update Requests sent to the alternative cellular communication network. This must be avoided since it could lead to congestion. In case of a 2G network, the congestion could occur either in the Base Station System (BSS) part due to Stand-alone Dedicated Control Channel (SDCCH) congestion or in the Mobile Switching Centre (MSC) or Serving GPRS Support Node (SGSN). In this latter case, the overload is caused by the high number of simultaneous Location Update/Routing Area Update procedures to be processed by these nodes. A further drawback of this solution is that the RNC of the network with the fault condition should be started up, again when the fault condition is over. Such a start up procedure generally is quite complicated and may therefore take a long time and/or result in further faults.